How To Make Custom Headers - Unfair Header Fabrication

We Build The Custom Headers For Our 1,400hp '69 Camaro Project Car.

Editor's note: This month's installment for Project Unfair (from Prodigy Customs and II Much Fabrication) deals with a familiar subject, but with an Unfair twist. We promised lots of tech and insight into the decisions and trade-offs of building this car, and headers are at once familiar, but also full of design choices. Read on to see how John Parsons and Frank Serafine decided on this particular header design.

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Project Unfair, our '69 uber Camaro needs a set of headers that can support 1,400 hp. That's a lot of horsepower, and as you might suspect, there isn't any ready-made solution, which means author Parsons had to make a custom set to meet Unfair's unusual requirements.

There is a bewildering array of design choices when making custom headers. We consulted the experts at Cone Engineering, Specialty Products Design, Burns Stainless, along with Jim Bell at Kenne-Bell (who manufactures the 3.6L supercharger that will assist in making all that power) and engine builder Pat Musi at Pat Musi Performance. We had originally planned on building tri-Y headers (see sidebar), but the consensus was that a traditional four-into-one header design would work better with the big huffer.

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With that major decision done, a whole new bunch of design decisions came into play: What primary tube diameter? Should the diameter be the same, or should it step up in size along the tube? How long should the primary tubes be? How important is getting all the tubes the same length? What size should the collector be? Is a merge collector important? What size should the exhaust beyond the collector be? And finally, what material should be used?

We quickly settled the material question by going with 304 stainless steel. It's an excellent alloy for headers as it resists corrosion at typical header temperatures, is easy to weld, and can be cut and fitted with the right tools, though the right saw is needed.

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With the material chosen, the next question is the header's primary tube diameter. There is a lot of information around about the importance of this parameter, and some of it is contradictory. Bell had sized some headers with his big supercharger and found that 2 1/8-inch primaries made the most power, but only about 20 hp more than 2-inch designs.

However, given the dual mode of the car (1,200-1,400 hp for drag racing and top-speed runs, 800 hp for road racing and auto-crossing), you also have to consider performance when operating at the lower horsepower. While too small of a primary tube restricts airflow, too large of a primary tube causes a drop in exhaust gas velocity, and likewise a decrease in performance. By compromising on the tube diameter, you are trying to get the best performance possible in each configuration using the same header, even though you'll forfeit maximum performance in one mode.

Given that, we turned to Rich Craig at Cone Engineering and discovered something else: 2-inch mandrel-bent stainless tube was widely available and reasonably priced, while 2 1/8-inch tube is less common and therefore much more expensive. Not only did the decision to go with 2-inch versus 2 1/8-inch tube work for performance, it also saved some cash-never a bad thing, even in a high-end build.

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Now comes the daunting task of trying to get 1,400 hp under the car and through a full exhaust. Basic airflow calculations (see sidebar) quickly show that a 4-inch dual exhaust is optimal for 1,400 hp, though a 3-inch exhaust is good enough for 800 hp. Not only is there a dual-mode constraint with the primary tube diameter in the headers, but now there's another one: how does one fit 4-inch tubing under a car that doesn't even have room for 3.5 inches? Compromise and ingenuity is how.

The first step is to figure out where the collectors will go. John spaced the collector as far outside as possible to make engine oil plumbing and transmission removal simpler.

Cone's cool band saw guide works by helping to place a straight line along the curved tube along the bend radius. Cutting on the bend radius means the tube opening will be round (not oval).

A bandsaw is the best kind of saw for stainless steel. John says, "I've tried a lot of saws over the years, and this bandsaw is the best way to cut mandrel bends. Don't waste your time and money with any kind of round saw blade."

A quick touch-up on a belt sander removes the saw marks.

It's almost ready for fitting, but the tube is slightly oval from the stress of mandrel bending.

Making the tube round again is accomplished by a vice and some pressure. It's a bit tricky to get the feel for when the tube moves back to a round shape and stays there, though the author does it in a couple of quick squeezes.

Another saw in his arsenal: John uses a Femi NG120 when making a 90-degree cut on straight tube, usually when cutting the "legs" off a mandrel bend.

Check out these cute little clamps from IC Engineering. No more messing around with masking tape or hose clamps.

The clamps pull double duty-they hold the tube pieces together well enough to check the tube routing, and...

...securely enough to tack-weld the tubes together.

However, sometimes space is too tight to use the clamps, so we went old-school and marked index lines across the cut.

Here you can see an index line mistake. After tack-welding, the tube didn't fit right, so we had to cut out the tack weld and try again.

Wait a minute. How did all four tubes end up in that particular routing? What's the secret for figuring out how to get all the tubes to go from the exhaust ports to the collector and end up about the same length? There's no one good answer, but John has a method he uses.

First, he routes the back port (cylinder 7, using the GM numbering method) forward and around to get enough length. Then he works out the height of that routing to either one of the outside locations in the collector.

Next, he routes the front port (cylinder 1) to its spot in the collector, trying to leave room for the two middle tubes.

After that, it's time to route the tube for cylinder 5. Since the collector is pushed outside, there is room to route this tube close to the block and around to the collector, leaving room for the last tube to snake its way to the collector.

Here's the final routing again, with all the tubes tacked together and ready for final welding.

This is the collector simulator again, now filled with stainless steel.

Quality welding of stainless steel means back-purging. This assembly supplies shielding gas (argon) to the back side of the weld.

Attention to detail in the cutting and fitting will result in perfect butt-fits of the tube ends to each other.

Once all the tubes are fully welded, it's time to secure them to head flanges. All the tubes are positioned and tack-welded to the flange...

...and tacked together inside the collector simulator.

Here's a better look at the tubes tacked to the flange after the nearly done header has been removed from the car.

If the tubes are placed squarely in the header flange, they should all be nearly flush with the inside edge of the flange.

This makes it easy to fully weld them to the inside edge.

This shot shows the relative sizes of 4-, 3.5-, and 3-inch collectors, along with Cone's cool inner tube merge setup.

The first step is cut all the tubes square and even with each other. Our Femi bandsaw makes short work of that task. Note how he left the collector simulator on to keep the tubes properly aligned until they are welded together.

After cutting and some cleanup with a file, the collector is ready to be welded together.

Project Unfair Camaro is under the knife again. This time the 1969 Chevy Camaro is getting equipped with a new traction control system. Only at www.superchevy.com, the official website for Super Chevy Magazine. » Read More